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\title{Role of Riverine Dissolved Organic and Inorganic Carbon and Nutrients in
Global-ocean Air-sea CO2 Fluxes}



\author[1]{Raphael Savelli}%
\author[2]{Dustin Carroll}%
\author[3]{Dimitris Menemenlis}%
\author[4]{Stephanie Dutkiewicz}%
\author[5]{Manfredi Manizza}%
\author[3]{A. Anthony Bloom}%
\author[6]{Karel Castro-Morales}%
\author[7]{Charles E. Miller}%
\author[8]{Marc Simard}%
\author[9]{Kevin W. Bowman}%
\author[3]{Hong Zhang}%
\affil[1]{Unknown}%
\affil[2]{Moss Landing Marine Laboratories, San José State University}%
\affil[3]{Jet Propulsion Laboratory, California Institute of Technology}%
\affil[4]{MIT}%
\affil[5]{Scripps Institution of Oceanography}%
\affil[6]{Friedrich Schiller University Jena}%
\affil[7]{Jet Propulsion Laboratory}%
\affil[8]{Caltech/Jet Propulsion Laboratory}%
\affil[9]{Jet Propulsion Lab (NASA)}%


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  \date{June 18, 2024}


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\begin{abstract}
While the preindustrial ocean was assumed to be in equilibrium with the
atmosphere, the modern ocean is a carbon sink, resulting from natural
variability and anthropogenic perturbations, such as fossil fuel
emissions and changes in riverine exports over the past two centuries.
Here we use a suite of sensitivity experiments based on the ECCO-Darwin
global-ocean biogeochemistry model to evaluate the response of air-sea
CO2 flux and carbon cycling to present-day lateral fluxes of carbon,
nitrogen, and silica. We generate a daily export product by combining
point-source freshwater discharge from JRA55-do with the Global NEWS 2
watershed model, accounting for lateral fluxes from 5171 watersheds
worldwide. From 2000 to 2019, carbon exports increase CO2 outgassing by
0.22 Pg C yr-1 via the solubility pump, while nitrogen exports increase
the ocean sink by 0.17 Pg C yr-1 due to phytoplankton fertilization. On
regional scales, exports to the Tropical Atlantic and Arctic Ocean are
dominated by organic carbon, which originates from terrestrial
vegetation and peats and increases CO2 outgassing (+10 and +20\%,
respectively). In contrast, Southeast Asia is dominated by nitrogen from
anthropogenic sources, such as agriculture and pollution, leading to
increased CO2 uptake (+7\%). Our results demonstrate that the magnitude
and composition of riverine exports, which are determined in part from
upstream watersheds and anthropogenic perturbations, substantially
impact present-day regional-to-global-ocean carbon cycling. Ultimately,
this work stresses that lateral fluxes must be included in ocean
biogeochemistry and Earth System Models to better constrain the
transport of carbon, nutrients, and metals across the
land-ocean-aquatic-continuum.%
\end{abstract}%



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